Ionic-size effect on the structure and Tc of T′-(R 1− xR′ x) 1.85Ce 0.15CuO 4 (R  Pr, Nd, Sm and Eu; R′  Gd and Y)

• Published in: Physica. C, Superconductivity Vol. 260; no. 1; pp. 117 - 124
• Main Authors: Meen, T.H., Yang, H.D., Huang, W.J., Chen, Y.C., Lee, W.H., Shieh, J.H., Ku, H.C.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1996
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/0921-4534(96)00135-9

(R 1− x R′ x ) 1.85Ce 0.15CuO 4 (R  Pr, Nd, Sm and Eu; R′  Gd and Y) have been investigated by means of X-ray diffraction, electrical-resistivity, and magnetic-susceptibility measurements. Lattice parameters a, c, and the unit-cell volume V decrease with increasing Gd or Y concentration x, and the decreasing rates with Y are larger than those with Gd. It is found that the critical concentration x c, at which the superconductivity disappears, depends on the ionic size of R, and the T c suppression rate for each system with Y doping is larger than that with Gd doping. Thus the effect of a small ionic radius for Y plays a much more important role than the large magnetic moment for Gd on the suppression of superconductivity in (R 1− x R′ x ) 1.85Ce 0.15CuO 4. From the observations of the deviation of the lattice parameters in R 1.85Ce 0.15CuO 4 and the rapid increase of | dln T c/d x | in (Eu 1− x Y x ) 1.85Ce 0.15CuO 4, the structural distortion boundar estimated to lie between Eu 1.85Ce 0.15CuO 4 and Gd 1.85Ce 0.15CuO 4. This provides clear evidence that the absence of superconductivity for Gd 1.85Ce 0.15CuO 4 is due to weak ferromagnetism in the CuO planes resulting from the too small ionic radius of Gd, which induces a lattice distortion in the T′ structure.